(3)
Comparison of LOO and WAIC : In regression problems, LOO requires simultaneous independence of {(Xi,Yi)},
whereas WAIC needs only conditional independence {(Yi|Xi)}. In this book, we give the mathematical proof of this fact.

Diagnosis: If LOO is different from WAIC, then leverage sample points are contained in the sample. A statistician had better
reconsider whether such points should be included in statistical inference or not.
Leverage sample points can be found because they make the pointwise functional variances larger.